1. Technical Field
The present invention relates to a drive shaft coupling for transfer of torsional force between a shaft and a rotatable element. The drive shaft coupling includes a rigid tube section and a flexible coupling member connected to the tube section, with at least two, in-series connected bellows segments that enable center axis deviations between the shaft and the rotatable element.
2. Background of the Invention
There is a permanent demand for reduced fuel consumption for all types of vehicles. One way to reduce fuel consumption is to lower the total weight of the vehicle, generally by using new material with lower weight than for corresponding traditional solutions. One example of such development is the use of composite material for parts of the power transmission of a vehicle from the motor/gearbox to the drive wheels. Thus, it is possible to produce a drive shaft with included flexible couplings manufactured from composite material.
U.S. Pat. No. 5,725,434 discloses a shaft of composite material with an integrated, elastically deformable coupling flange enabling center axis deviations at the mounting end of the shaft. A problem with this known drive shaft coupling is that it is comparatively bulky, as the coupling flange is radially large.
U.S. Pat. No. 4,173,128 disclose a shaft laminated of composite material with flexible coupling sections adjacent the ends of the shaft. These flexible-coupling sections include, in series, coupled bellows with identical geometry and elasticity for bending. The need for space is reduced radially by using in-series coupled bellows. It has come to be appreciated, however, that this type of drive shaft coupling is less suitable for uses where the center axis deviations between bellows is comparatively large and high torque occurs. One example of such over-burdening use is as propeller shafts for heavy trucks.
In one aspect, the present invention takes the form of a provision of a drive shaft coupling with a small space requirements and which copes with large angle movements as well as high torsion. In this regard, the invention includes a drive shaft coupling having two adjacent bellows segments of different flexural resistance. The bellows segment nearest a tube section connected thereto presents less flexural resistance than the immediate following bellows segment. By this design of the drive shaft coupling, each individual bellows segment may be dimensioned in such a way that stress is distributed evenly over all bellows segments so that the component may be optimized; for example, with respect to installation and strength. Another improvement over known universal joint shafts is an increased freedom for installation of the driveline. A shaft designed according to the present invention does not need to have equal angle of articulation in the bellows as a universal joint shaft has in known universal joint designs.
In one embodiment of the invention, the variations in flexural resistance between two adjacent bellows segments may be produced by variations in the thickness of material of the bellows segments. Alternatively, these variations may be produced by variations in the outside diameter of the bellows segments.
In another embodiment of the invention, the variations in flexural resistance between two adjacent bellows segments are produced by variations in the inside diameter of the bellows segments. Alternatively, these variations may be produced by variation of the radial angles of each bellows diaphragm in relation to the longitudinal axis of the coupling member.
In still another embodiment of the invention, the variations in flexural resistance between in-series connected bellows segments are produced by variation of the distance between adjacently positioned bellows segments.
According to a preferred embodiment of the invention, the coupling member is manufactured from an epoxy composite with a mixture of glass fiber and carbon fiber. The variations in flexural resistance between two adjacent bellows segments can then be produced by variation of the fiber direction in the composite material.
Still further, the tube section and the coupling member may be manufactured in one piece from steel.